The present invention relates generally to wellbore systems for obtaining cores from wellbores and, more specifically, to system and methods especially suitable for improved drilling operation as well as for obtaining large diameter cores in unconsolidated formations.
In oil fields with unconsolidated formations, cores are more likely to be washed out or lost prior to retrieval. In such formations, it is desirable to utilize coring tools capable of retrieving larger diameter cores in order to improve the likelihood of obtaining suitable cores. For instance, it is desirable to obtain cores with sufficient mass to permit an analysis of gas and/or hydrocarbon fluid content. Larger diameter core samples are more useful for such purposes.
In order to obtain large diameter cores, e.g., cores greater than two and seven eighths inches in diameter when drilling wellbores diameters in the range of six inches, mining exploration rigs have been utilized in the prior art. The mining industry utilizes a wire line coring system that delivers a two and seven eighths inch core ten feet in length. Mining exploration rigs are hybrids of small service rigs and are primarily meant for shallow soft drilling most often associated with the mining industry as compared to deeper, harder formations of hydrocarbon wells in the oil and gas industry. One of the leading problems of mining exploration rigs that are used to retrieve large diameter cores arises from the use of casing as the drill string rather than standard API drill pipe. Standard API drill pipe does not have a large enough inner diameter to obtain the size cores desired. Casing is normally used to case or line the borehole for production of the well and is not desirable for use in drilling. Casing has less torsional strength than drill pipe. When rough drilling conditions are encountered, the casing is likely to twist off thereby resulting in expensive fishing jobs. For instance, casing suitable for coring six and one-quarter inch diameter wellbores may typically have a maximum torque value of about six thousand foot-pounds which is much less than drill pipe. The tensile strength of a casing string is also considerably less than drill pipe and may be in the range of about 300,000 pounds.
Another problem with use of casing for coring operations is that special rig modifications are needed to operate casing strings as compared to standard API drill strings. The mining exploration rigs are generally unsuitable for operating API drill pipe and may typically require an entire rig replacement in order to drill deeper after the coring operation is completed. It is well known that each stand of drill pipe has upsets which may be utilized by drilling rigs whereas the casing does not have upsets. Thus, different gripping equipment, such as dog collars must be used each time casing is used due to the lack of upsets. Use of casing as the drilling string in a coring operation therefore typically requires a specialized core rig which is limited in the amount of weight and torque available for drilling thereby resulting in slower drilling rates than conventional drilling rigs that utilize drill pipe. The rates of drilling may be as much as ten times greater when using drill pipe as compared to casing. Thus, rig costs may be significantly increased when utilizing casing for drilling purposes.
Consequently, there remains a need to provide an improved system for obtaining large diameter cores and/or other wellbore operations without the significantly time consuming and costly disadvantages associated with the use of casing in coring and/or drilling strings. Those of skill in the art will appreciate the present invention which addresses the above and other problems.
An objective of the present invention is to provide an improved coring and/or drilling assembly and method.
Another objective of an embodiment of this invention is to provide a coring system that may be utilized with a drilling rig capable of handling standard API drill pipe.
These and other objectives, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. However, it will be understood that above-listed objectives and/or advantages of the invention are intended only as an aid in quickly understanding aspects of the invention, are not intended to limit the invention in any way, and therefore do not form a comprehensive or restrictive list of objectives, and/or features, and/or advantages.
Accordingly, the invention comprises, in one embodiment thereof an assembly operable for drilling and/or coring a wellbore and/or other operations. The assembly may comprise one or more elements such as, for instance, a drill pipe having a tubular outer diameter, an upset portion of the drill pipe tubular extending radially outwardly with respect to the tubular outer diameter wherein the upset portion has an outer diameter ranging from five and one-half inches to six and one-half inches, the drill pipe having an inner diameter ranging from three and three-quarter inches to four and three-quarter inches, and a threaded pin connection for the drill pipe adjacent the upset portion wherein the threaded pin connection has an axial length ranging from two and three-quarters to three and three-quarters inches.
The assembly may comprise a tubular outer diameter in the range of about five inches. The assembly may further comprise a coring tool insertable into the drill pipe tubular, and an inner core barrel of the coring tool for receiving a core sample wherein the inner core barrel has an inner diameter greater than two and seven-eighths inches. In another embodiment, the inner core barrel has an inner diameter equal to or greater than three inches. In another embodiment, the inner core barrel has an inner diameter ranging from three inches to three and one-half inches.
The assembly may further comprise a plurality of the drill pipe tubulars threadably connected together to form a drilling string. The drilling string may have a maximum torque value without damaging the drilling string greater than thirty thousand foot pounds. In another embodiment, the maximum torque value is greater than fifty thousand foot pounds. In one embodiment, the drilling string may have a maximum tensile value without damaging the drilling string greater than four hundred thousand pounds. In another embodiment, the drilling string has a maximum tensile value without damaging the drilling string greater than five hundred thousand pounds.
A method for a coring system in accord with the present invention comprises one or more steps such as, for instance, providing a plurality of drill pipe tubulars having a minimum inner diameter greater than or equal to three and three-quarter inches, providing an upset on the drill pipe having a maximum outer diameter less than or equal to six and one-half inches, and providing a coring tool having a core barrel for receiving a core with an outer diameter greater than or equal to two and seven-eighths inches.
The method may further comprise providing a threaded pin adjacent the upset having a maximum axial length of three and three-quarters inches. The method may further comprise providing the barrel axial length is greater than twenty feet. The method may further comprise providing that the drilling string has a maximum torque value without damaging the drilling string of greater than thirty thousand foot pounds. In another embodiment, the maximum torque may be greater than fifty thousand foot pounds. The method may further comprise providing that the drilling string has a maximum tensile value without damaging the drilling string of greater than four hundred thousand pounds.
The method may further comprise providing that the drilling string has a maximum tensile value without damaging the drilling string of greater than five hundred thousand pounds. The method may further comprise providing that the coring tool is wireline retrievable.
In another embodiment an assembly is provided that is operable for coring and/or drilling and/or other operations in a wellbore less than seven inches in diameter comprising one or more elements such as, for instance, a plurality of drill pipe tubulars threadably connectable together wherein each drill pipe tubular having a tubular outer diameter, an upset for each of the drill pipe tubulars having a maximum outer diameter less than or equal to six and one-half inches, and each drill pipe tubular having an inner diameter greater than or equal to three and three-quarter inches.
The assembly may further comprise a threaded pin connection wherein the axial length of the pin may be less than three and three-quarter inches in length. The assembly may further comprise a coring tool with an inner coring barrel for receiving a core having an inner diameter for receiving a core greater than or equal to two and seven-eights inches in diameter.
This summary is not intended to be a limitation with respect to the features of the invention as claimed, and this and other objects can be more readily observed and understood in the detailed description of the preferred embodiment and in the claims.